ABSTRACT This proposal investigates the contribution of defective maintenance of protein homeostasis (proteostasis) in the steatotic liver, to the progression to hepatocellular carcinoma (HCC). Disturbances in the systems that maintain liver proteostasis have been observed in HCC, but the extent to which loss of proteostasis in the steatotic liver constitutes a risk factor for development of HCC remains unknown. We will focus in chaperone- mediated autophagy (CMA), a protein quality control system that mediates selective degradation of cytosolic proteins in lysosomes. Defective CMA in liver leads to hepatosteatosis due to alterations in hepatic glucose and lipid metabolism and in overall energetics. Our recent studies on the interplay between CMA and oncogenesis have shown that: (I) CMA has an anti-oncogenic effect since failure of CMA, such as that observed in aging, diabetes or the steatotic liver, favors malignant transformation, and mice with hepatic CMA blockage develop spontaneous tumors; (II) CMA is required in transformed cells to sustain tumor growth since: (i) transformed cells maximally upregulate CMA, (ii) blockage of CMA in transformed cells reduces proliferation and induces cell death and (iii) blockage of CMA in pre-formed tumors inhibits tumor growth and results in tumor shrinkage. We propose that 1) the gradual decline of CMA in the steatotic liver facilitates malignant transformation in the context of a pro-oncogenic stimulus and that 2) interventions to restore normal CMA activity in the steatotic liver will prevent or slow down progression to HCC. To test this hypothesis, we intend to: 1) determine the contribution of CMA failure to oncogenic transformation in HCC; 2) identify the liver and immune cell type-specific contribution of CMA failure to HCC progression; 3) evaluate the possible beneficial impact of chemical and genetic upregulation of CMA as a preventive intervention against NASH to HCC progression. Significance: This study will elucidate how functional impairment of CMA contributes to liver pathology and if it increases HCC risk in steatotic liver. Our findings could help in developing new approaches to preserve steatotic liver homeostasis and function and reduce its risk to HCC.